Nowadays, a large amount of analyses are carried out by combining high resolution separation techniques and mass spectrometry. This combination of scientific instruments has become important in different domains such as those requiring a high quantity of analyses, due partly to the development of new molecules. This is particularly true for fields such as the pharmaceutical, environmental and proteomic industries.
The coupling of chromatography and mass spectrometry now achieves the highest molecular analysis performance. Different coupling and ionisation techniques have been developed using liquid chromatography and mass spectrometry. One such technique is called Atmospheric Pressure Chemical Ionization (hereinafter APCI). According to this technique, the sample and the mobile phase are first nebulized and dried at atmospheric pressure and then ionized by a corona discharge. One drawback of this technique is the use of a liquid mobile phase which introduces cross-contamination of the samples. Another well-known type of ionization source is called Matrix Assisted Laser Desorption Ionization, or MALDI. In this case, desorption and ionization of a solid state target material are induced simultaneously by heating the sample directly with a laser. The ionization process is carried out at atmospheric pressure or under vacuum via a matrix. Again, cross-contamination is introduced in the sample from the matrix. For both of these techniques, sample preparation and analysis are time consuming and contribute to most of the analysis cost.
In the prior art, various desorption and ionization techniques are found that aim at improving the basic APCI and MALDI approaches described above. For example, U.S. Pat. No. 6,747,274 (LI) discloses a technique employing numerous lasers operating in tandem on samples for increasing the throughput of MALDI-type apparatus. U.S. Pat. No. 6,630,664 (SYAGE et al.) proposes an apparatus for photoionizing a sample that is circulating in an ionization chamber. The sample is ionized by a light source and electrodes direct the ionized sample to a mass spectrometer for analysis. U.S. patent application published under no. 2004/0245450 (HUTCHENS et al.) discloses another MALDI-type system. This technique does not, however, solve the issue of cross-contamination from the matrix. The desirability of having no matrix is actually mentioned by Hutchens, but he does not elaborate on an apparatus or method for enabling such a matrix-free technique.
In U.S. Pat. No. 6,288,390 (SIUZDAK et al.) there is disclosed a method for desorbing and ionizing an analyte, which has been “loaded” onto a porous semi-conductor. Lasers irradiate the analyte-loaded semi-conductor to cause the analyte to desorb and ionize under reduced pressure. The absence of a matrix makes the preparation of each sample analyte less complicated than for the MALDI technique.
In summary, the prior art teaches various techniques for vaporizing and ionizing a sample of a substance, but these techniques are often hampered by extensive and complicated preparation steps, the risk of cross contamination between samples, the need for additional substances for composing the matrix and liquid mobile phase, or other effects of having a matrix or a liquid phase involved in the technique. There is therefore a need for a technique alleviating these drawbacks of the prior art.